Field of the Invention
The invention relates to a method and device for improved localization of a vehicle from a stationary reference map.
Description of the Background Art
Systems are used in vehicles, in particular motor vehicles, which require information about the existence of objects in the environment surrounding the vehicle, as well as information on the position and dimension of said vehicle. Information on a vehicle's surroundings, in particular to distinguish between streets, open spaces and obstacles, is necessary for navigating in an unknown area. It can also be used as an input parameter for autonomous assistance systems such as automatic parking aids or parking assistance systems, brake assists and accident preparation systems.
Today, more and more vehicles are being developed which run from partially automated to highly or fully-automated. A crucial aspect in this respect is the location of the vehicle relative to objects in the surrounding environment.
From the prior art, different measurement methods are known which are used to identify the environment and to pinpoint streets, open spaces and obstacles. Most of these are based on measuring the runtime of a pulse that is sent out from the vehicle and which reflects back from objects. For example, ultrasound measurements are very widespread.
From the publication DE 103 37 845 A1, a control assembly for a vehicle and a method for identifying a vehicle position on a roadway are known. Ultrasound or radar sensors are hereby sometimes affixed to the sides of the vehicle to also measure the area in the lateral surroundings of the vehicle. Roadside and roadway are identified from the impulse response measurements. The control signals resulting therefrom are then aimed to be conveyed to assistance systems, for example, for accident prevention or for parking assistance.
From the publication DE 10 2010 013 647 A1, which corresponds to U.S. 2010/0256835, another method is known for controlling multiple vehicles which drive in a convoy consisting of a lead vehicle and several vehicles. The vehicles are piloted by means of vehicle-to-vehicle communication and by the detection of position coordinates, wherein the vehicles always follow the lead vehicle and autonomously pilot their position using their relative position to the lead vehicle. The current positions of a vehicle in the convoy are thereby identified by means of vehicle-to-vehicle communication und a global positioning device, wherein the monitoring of the vehicle positions commanded by the lead vehicle occurs by monitoring the distance between the vehicles. The predetermined vehicle distance can be dynamically assigned, for example, per criteria such as vehicle speed, braking properties, weather conditions, street condition or fuel consumption.
Furthermore, from the prior art, systems are known which feature cameras built into the vehicle, for example front cameras, which utilize road signs, lane markings, etc. to find unique characteristics in the picture. This way, so-called landmarks can be placed on a reference map. This makes it possible to highly accurately identify the position in all subsequent trips using the current image features as they relate to the reference map. When using camera-based systems to identify landmarks, for example, poor visibility, darkness, reoccurring image content and a small opening angle of the camera can diminish robustness.
From the field of robotics, a method for tracking autonomous robots by means of a radar using so-called SLAM methods (Simultaneous Location and Mapping) is known. Although SLAM methods are mostly independent of weather conditions, they do not provide unambiguous features and are highly bound to a known, statistical geometry of the surrounding structure.
The known systems are able to, at least rudimentarily, determine the positions of objects in the area surrounding the vehicle. It is also possible to identify a vehicle position from a reference map when there is low accuracy. Object positions exclusively identified by odometry prove to be too inaccurate. Positions identified by a satellite information system, e.g. GPS/D-GPS (GPS-Global Positioning System; D-GPS Differential Global Positioning System) are just as inaccurate and furthermore not available, for example, in parking garages. Therefore, the positions thus identified do not meet the demands of future, autonomously navigating and operating assistance and control systems in vehicles.